1. Field
The present invention relates to a stepless variable auto stroke hydraulic breaker system and, more particularly, to a stepless variable auto stroke hydraulic breaker system capable of reducing impact energy reflected in the event of an idle blow by detecting, via a vibration sensor, a frequency or the number of vibrations generated when a chisel breaks objects such as bedrocks, operating with a short stroke if the frequency or the number of vibrations does not exceed a preset frequency or a preset number, and automatically switching the short stroke into a long stroke if the frequency or the number of vibrations exceeds the preset frequency or the preset number.
2. Description of the Related Art
In general, hydraulic breakers are used to break up rocks. Such a hydraulic breaker includes a housing that has a reciprocating piston controlled by a distribution valve and a cylinder bore, and a pressure accumulator. While the hydraulic breaker is in operation, the pressure accumulator is preliminarily pressurized to a pre-load pressure in order to prevent the hydraulic breaker from being damaged by a fluid cavity and a pressure gradient and increase performance of the hydraulic breaker, and transmits a blow to a chisel from the piston. Thereby, a chisel tip supplied with kinetic energy of the piston breaks a rock.
In the case of a rock composed of soft substances, energy remaining after the rock is broken is applied to components of the hydraulic breaker.
Therefore, a process in which applied kinetic energy is greater than energy required to break the rock is not desirable, because high stress occurs at the hydraulic breaker due to the energy remaining after the rock is broken. Thus, applying a rapid change in the kinetic energy to all operating conditions prolongs a life of the hydraulic breaker and is simultaneously an important requirement for optimal material breaking.
However, the conventional hydraulic breakers are driven before a supplied hydraulic pressure reaches a level higher than or equal to the pre-load pressure of the pressure accumulator, or are continuously driven after the supplied hydraulic pressure is reduced below the pre-load pressure of the pressure accumulator. That is, the pressure accumulator cannot be operated with precision. In detail, the pressure accumulator cannot absorb an undesired pressure gradient, cannot prevent a cavity in a hydraulic fluid, and cannot increase a flow of the fluid during an operating stroke of the piston. Therefore, there is a serious risk of certain portions of the impact mechanism being damaged.
To solve this problem, Korean Patent No. 10-1285062 has been proposed.
The preceding patent includes a housing 10 with a cylinder bore 11, a forward working chamber 23 and a rear working chamber 18, a hydraulic fluid supply passage 26 continuously connected to the forward working chamber 23 and a drain passage 33 connected to the rear working chamber 18, a hammer piston 12 reciprocally guided in the cylinder bore 11 in order to deliver hammer blows to a working implement 14 attached to the housing 10, a pressure accumulator 27 pre-loaded to a certain pressure level, and a distribution valve 30 for alternatingly connecting the rear working chamber 18 to the drain passage 33 and the supply passage 26 to thereby reciprocate the hammer piston 12, wherein a sequence valve 34 is provided in the drain passage 33 for the purpose of keeping the pressure in the rear working chamber 18 at such a level that the resulting forward directed force will prevent the piston 12 from being moved backward in the cylinder bore 11 at pressure levels in the supply passage 26 below the pre-load pressure level of the accumulator 27. Thereby, impact energy according to an idle blow is reduced.
However, the preceding patent has a problem in that it is still insufficient to reduce the reflected impact energy according to the idle blow.